The present invention relates to a nailing machine and holder and more particularly to a nailing machine and holder in which compressed fluid is used to move a driving member in the nailing machine to drive a nail.
In certain kinds of nailing machines, nails are driven by a driver incorporated in a piston driven within a cylinder by high-pressure compressed fluid. The fluid is rapidly introduced into an upper portion of the cylinder so that the piston within the cylinder is driven downward by the pressure of the compressed fluid to hit a nail set in an injection portion to thereby inject the nail toward and into a driven member. However, the pressure of the high-pressure fluid introduced into the cylinder not only acts on the upper surface of the piston to drive the piston downward, but also acts on the opposing upper bottom surface of the cylinder. Accordingly, the cylinder is lifted up by the reaction force of the fluid pressure so that the cylinder housing tends to jump up separating the forward end of the injection portion from the surface of the driven member so that it is difficult to perform exact driving.
In order to prevent such jumping-up, nailing may be done while the upper portion of the cylinder housing is pressed down by hand. However, the driving depth of the nail changes in response to the magnitude of the pressing force, and accordingly, in the conventional nailing machine, the driving depth of the nail changes depending on whether the cylinder housing or is not pressed. When pressed, the driving depth changes corresponding to the magnitude of the pressing force. For example, when a gypsum board is nailed onto a wood surface, the nail head often projects too much from the surface of the gypsum board or sinks into the gypsum board too deeply to break a sheet of paper provided at the surface of the gypsum board. If the nail head projects too much, the nail head will interfere with the work of covering the gypsum board with cloth. If the nail head sinks too deep, the shape-retaining force of the gypsum board will be lost. Therefore, in the conventional nailing machine, controlling the depth of penetration of the nail is difficult. It is therefore desirable to have a nailing machine in which the nail is always driven exactly and uniformly to a certain depth.
Generally, when a nailing machine is operated, a rebound results as compressed air forced into the cylinder acts on the upper surface of the nail-driving member within the cylinder to move the driving member downward, and the compressed air acts as a reaction force on the upper wall of the cylinder to move the cylinder upward. When the nailing machine is moved upward by the rebound, a bottom dead point of the nail-driving member is moved upward, so that the impact force is reduced. Of course, the influence of the rebound can be reduced by a worker pressing the nail machine onto the driven member to control the quantity of displacement of the nailing machine. However, in this situation uniform driving is impossible because the driving force changes corresponding to the magnitude of the pressing force.
Generally, in the conventional nailing machine for driving a nail having a round-form enlarged head portion, the inner diameter of the nose portion for driving out the nail is established to be slightly larger than the diameter of the head portion of the nail. Thus, because the forward end portion of the nail can move freely within the nose portion, the nail is driven obliquely. This tendency is remarkable in a gypsum board nail which is larger in head diameter than an ordinary nail. Furthermore, gypsum board requires a nail to be driven in a perpendicular posture more exactly than the ordinary nail, because reinforcement paper on the surface of the gypsum board may be broken by the edge of an inclined nail head.
Therefore, a holding-guiding mechanism for guiding the forward end portion of a nail driven out by the nose portion of the nailing machine to the central position of the nose portion and for holding the nail in a perpendicular posture has been proposed, for example, as disclosed in Japanese Patent Post-Examination Publication No. 56-20153 (1981). However, because the nail holding-guiding mechanism is provided in the inside of the nose portion of the nailing machine, the outer diameter of the nose portion is rather large, and it is difficult to ascertain where the nail-driving portion is. Consequently, handling of the nail machine is somewhat difficult.
The same technique as described above has also been disclosed in Japanese Utility Model Unexamined Publication No. 51-79783 (1976). Because the nail holding-guiding mechanism partly projects at the forward end of the nail-driving-out nose portion, the holding-guiding elements are arranged to be in direct contact with the surface of the driven member. When, for example, the position of the nose portion is shifted laterally, the holding-guiding elements are opened, so that the nail may be inclined. When, for example, the nail is rapidly driven out, the respective holding-guiding elements are impulsively opened. Because the nailing machine has no means for preventing the opening of the respective elements, an elastic member urging the elements to be closed is excessively expanded and displaced. Consequently, durability is impaired.